Conventionally, as a luster pigment exhibiting pearl luster (hereinafter referred also to as a pearl luster pigment), there have been flaky particles, such as mica, synthetic mica, talc, flaky glass, flaky silica and flaky bismuth oxychloride, each coated with a metallic oxide such as a titanium oxide and an iron oxide. Flaky particles coated with two or more layers of these metallic oxides also have been proposed (see, for example, “Ganryo no Jiten” (Dictionary of Pigments), First edition, edited by Seiji ITO, published by Asakura Publishing Co., Ltd, Sep. 25, 2000, pp 239-241).
As a luster pigment exhibiting metallic luster (hereinafter referred also to as a metallic luster pigment), there have been flaky particles, such as flaky glass, mica and synthetic mica, each coated with a metal such as silver, gold and nickel (see, for example, JP 62 (1987)-175045 Y and JP 04 (1992)-2636 A).
Metallic luster pigments are not limited only to the flaky particles coated with metals or metallic oxides as described above. Some of the metallic luster pigments are made from flaky particles themselves made of metals such as aluminum and copper with no coating on their surfaces (see, for example, “Ganryo no Jiten” (Dictionary of Pigments), First edition, edited by Seiji ITO, published by Asakura Publishing Co., Ltd, Sep. 25, 2000, pp 232-234). Fish scale foil and flaky bismuth oxychloride themselves are sometimes used as pearl luster pigments (see, for example, “Ganryo no Jiten” (Dictionary of Pigments), First edition, edited by Seijiro ITO, published by Asakura Publishing Co., Ltd, Sep. 25, 2000, pp 239-241).
The luster pigments employing the flaky particles as described above (hereinafter, these luster pigments simply may be referred to as pigments) reflect light on their smooth surfaces and thus exhibit a satisfactory lustrous appearance.
Furthermore, a lustrous coating composition has been proposed in which the particle size of a luster pigment is adjusted so as to obtain a lustrous appearance and to prevent a filter from clogging during circulation for coating (see, for example, JP 2002-155240 A).
However, flaky particles used for conventional luster pigments each have a wide range of particle size distribution and have a high content of fine particles and coarse particles. Therefore, not only pigments made from flaky particles themselves but also pigments made from flaky particles coated with metallic layers and/or metallic oxide layers each have a wide range of particle size distribution.
Assume, for example, a case where a pearl luster pigment is produced by using flaky particles with a wide range of particle size distribution (that is, having a high content of fine particles and coarse particles) as a substrate and coating the substrate with a high refractive material such as titanium oxide. A high content of fine particles in the pigment causes a problem such as a decrease in lustrous appearance or a smooth and flat appearance without any particulate appearance. On the other hand, a high content of coarse particles in the pigment causes other problems. For example, a filter clogs when a coating composition containing this pearl luster pigment is filtered, the pigment particles are not oriented regularly in a coating film obtained by applying the coating composition and thereby a part of the pigment particles protrude through the film, and excessively large particles of the pigment are detectable as foreign substances in the coating.
Furthermore, even if the particle size of a luster pigment is adjusted as proposed in JP 2002-155240 A, it is difficult to realize a luster pigment capable of solving these problems completely. That is, it is difficult to realize a luster pigment having a good balance between desirable properties of achieving satisfactory lustrous appearance and particulate appearance and of inhibiting more reliably filter clogging and detection of foreign substances.